1969 Ford Mustang cooling

If it's cool while your moving, but over heats if you sit in one place I would guess that it is your fan system. You're likely right on the money with your thoughts about a fan shroud. If you can find a good twin electric fan with shroud that will match well with your radiator, then I would go that route...I personally think it looks cleaner on the engine bay. On a side note, you may want a slightly hotter thermostat... remember your oil temperature has to reach above 200 degree or it will slowly get contaminated by water. Also you need to be careful what oil you're buying. A lot of newer oils have drastically reduced the ZDDP, on account of newer engines don't have the same pressure on the CAMs as older engines used to have. Without it your engine will wear out your cam faster.

Yes no fan shroud could cause that. The fan is just blowing air every which way when your at a stop, the shroud would channel the air into the rad.